Two-Body Origin of Recombination-Induced Photocurrent Signals for Drift Velocity Resolution in Perovskite Solar Cells

Recombination-induced nonlinear photocurrent (NLPC) spectroscopy enables the resolution of nanosecond-scale charge transport in thin-film perovskite photovoltaic cells. In this pump–probe-like method, the first laser pulse initiates carrier drift to the electrodes, while the second pulse probes the transient carrier concentration remaining in the active layer via a saturation effect, wherein carriers excited by separate pulses interact and recombine on the ∼100 ps time scale. The two-body nature of the signal generation mechanism has typically been confirmed through standalone control experiments rather than by characterizing the response alongside the dynamics in a single measurement. Here, we vary both the delay times and laser fluence in NLPC experiments conducted on MAPbI3-based devices to confirm that the nonlinearity originates from two-body recombination processes involving independently excited carrier populations. In addition, a simplified model is introduced to capture the behaviors underlying the responses of MAPbI3 photovoltaic devices while remaining practical for data analysis and interpretation. To place the NLPC results in the context of related methods, our analysis suggests that recombination-induced and higher-order perturbative NLPC-like action spectroscopies provide equivalent time-of-flight information when carrier recombination is fast compared to charge transport across the illuminated region of the active layer. Together, the experiments and modeling framework presented in this work clarify the capabilities and limitations of NLPC spectroscopy for measurements of charge transport in thin-film photovoltaic devices.